1. Field of the Invention
The present invention relates to an eccentric vibrating mill having at least one grinding container to which as exciter unit is solidly attached and which serves as a vibrating drive.
2. Description of the Related Art
As is known, vibrating mills comprise cylindrical, trough-shaped or hopper-shaded containers, freely swivel-mounted on rubber buffers or springs, which are displaced into substantially circular swinging movements either by means of one exciter revolving in the mass centre, or by means of several exciters in the form of flyweights aligned on the mass centre. Impacts, which penetrate inside the grinding element filling by impulse propagation, are sent to the grinding elements housed in the grinding containers. Crushing is carried out by impact and friction action between the grinding elements themselves and between the grinding elements and the container wall. The mill filling describes a circular movement against the work direction of the exciter, ensuring conveyance of the grinding material.
In all contemporary vibrating mill designs--finishing programs of the companies: KHD Humbold Wedag AG, Cologne; Aulmann und Beckschulte, Maschincnfabrik Bergneustadt; Siebtechnik GmbH Maschincn-und Apparatebau, Mullheim/Ruhr; IBAG, Neustadt/Weinstra.beta.e; Ratzinger GmbH, Munich--the eccentric exciter is located in the mass centre of the machines so that the process can start with a circular vibration.
Suggestions for the construction of vibrating mills are known from the patent literature, in which the eccentric exciter or exciters is/are arranged outside the mass centre for structural reasons, but which in any case endeavour to describe a circular swinging movement. U.S. Pat. No. 3,545,688 describes a single-valve vibrating mill in which the grinding tube is set in circular vibration on both sides by two horizontally disposed eccentric motors. The object of DE Pat. No. 34 04 942 A1 is a `grinding device for crushing of coarse material`. The following explanation is given: `During operation the grinding device according to the present invention is set in circular vibration by means of the eccentric exciters attached to the housing . . . `.
A similar construction principle is the object of U.S. Pat. No. 3,425,670. The grinding container is here additionally compelled by horizontal support springs located on either side, enabling only vertical, elliptical vibrations, which tend to place a strain on the grinding material in the sense of a pounding effect. As already applies to DE No. 34 04 942, the drive is located in the gravity axis. U.S. Pat. No. 3,391,872 describes as a `Vibrating Grinding Mill` another device in which two eccentric exciters revolving against each other are arranged both outside and inside the gravity axis of the grinding apparatus. The focus here is on the principle of the `dive` mill (ball mill), in which, for the purpose of improving the grinding effect, the usual rotation of the grinding container is overlaid around the horizontal axis by linear vibrations, caused by both eccentric exciters revolving against one another. The direction of rotation of the grinding element filling is actuated by rotation of the grinding container and this may occur either freely (as a result of the directed linear vibrations) or forced (by means of an additional rotational drive), and not by means of the centrifugal acceleration of the flyweights in standard vibrating mills.
The unpublished DE Pat. No. 42 42 654 A1 describes a process for wet fine grinding and dry fine grinding using a linear trough vibrating mill which comprises two superposed grinding containers mounted on vibrating support elements, in which two exciter units are arranged eccentrically on one side outside the gravity axis and the mass centre of both grinding containers, as in FIGS. 1 and 2. Exciter unit and grinding container are located between the spring axes on the drive side and opposite the drive.
The abovementioned suggestions could not be carried into effect, since, compared to industrially used vibrating mills, they offer no advantage with respect to throughput and specific energy requirement.
A 1992 monograph: Kurrer, K.-E. et al.: `Analyse von Rohrschwingungmuhlen` [Analysis of tube vibrating mills], Continuing Reports VDI, Processing Technology Series No. 282, VDI Verlag 1992, presents research on directions of movement of mill filling and machine dynamics. According to this the grinding space of tube vibrating mills is divided into energy-rich and energy-depleted zones (p. 15 ff.). The energy-richest zone, the main stress zone, is characterised by the strongest normal impact and friction impact force (p. 57 ff.). The friction impact force is the prerequisite for the circular movement of the mill filling. The circular movement of the mill filling runs opposite to the direction of rotation of the exciter. In the case of the normal circular vibration of vibrating mills the mill filling can rotate either in a clockwise or an anticlockwise direction, according to the direction of rotation of the exciter.